A model for the hyperprothrombinemia in prothrombin 20210G/A heterozygotes.

Prothrombin 20210G/A heterozygotes transcribe equal quantities of RNA from the wild-type (right) and mutant genes (left). Nascent prothrombin 20210G mRNA is polyadenylated at positions 20210 and 20212 in the indicated ratio; by comparison, the 20210A mRNA is polyadenylated exclusively at position 20210. Prothrombin mRNAs that are polyadenylated at positions 20210 and 20212 translate with high and low efficiencies, respectively (illustrated by dense and sparse ribosomal loading).